PROCEEDINGS OF THE OHIO ACADEMY OF SCIENCE 121 



be of little assistance beyond suggesting the way in which 

 evolution did not take place. 



The experiments on the basis of Pure Line Breeding 

 belong to a comparatively recent period and are of the 

 utmost importance. Johannsen in 1903 published results 

 based on a pure line of beans self-fertilized for successive 

 generations, and evidently homozygous. From a bean 

 weighing 95 centigrams and far above the average in size 

 he obtained plants producing beans varying in weight from 

 approximately 35 to 70 centigrams but all far below the 

 weight of the parent. Utilizing these in turn as parental 

 forms, from those having a weight of 35-40 centigrams, 

 there resulted a progeny with an average of 57.2 centi- 

 grams, while from those having a weight of 65-70 centi- 

 grams a progeny was obtained which had an average of 

 55.5 centigrams. In other words, selection had not only 

 failed to make any advancement but actually resulted in a 

 slight retrogression. Facts quite in accord with this but 

 giving much more pronounced results have been obtained 

 by Tower (1906), Jennings (1908), Johannsen (1909) and 

 others. It should be noted, however, that there have been 

 several experiments, notably those of DeVries with butter- 

 cups. Tower with potato beetles, and Smith with Indian 

 corn, where a possible advance in a character resulted in a 

 group. Heterozygotes here may have been responsible for 

 the result although again the explanation may consist in the 

 elimination of the effects of a determiner. 



The results in mixed races as exemplified by corn, 

 beans, etc., where selection has gradually improved a group 

 of organisms but finally reached a limit beyond which no 

 progress appeared possible are comparatively well under- 

 stood and are due, as explained by Shull (1908), to the 

 separation of the pure lines which were present in the race 

 at the beginning. This is where the average agriculturist, 

 horticulturist and animal breeder has gone far astray, and, 

 having succeeded for a few generations in making progress, 

 has failed to understand why he may not continue to be 

 successful. 



